application/mov/match/fee_strategy.go

   1 package match
   2
   3 import (
   4         "math"
   5
   6         "github.com/bytom/vapor/errors"
   7         "github.com/bytom/vapor/protocol/bc"
   8 )
   9
  10 var (
  11         // ErrAmountOfFeeOutOfRange represent The fee charged is out of range
  12         ErrAmountOfFeeOutOfRange = errors.New("amount of fee is out of range")
  13 )
  14
  15 // AllocatedAssets represent reallocated assets after calculating fees
  16 type AllocatedAssets struct {
  17         Receives []*bc.AssetAmount
  18         Refunds  []RefundAssets
  19         Fees     []*bc.AssetAmount
  20 }
  21
  22 // RefundAssets represent alias for assetAmount array, because each transaction participant can be refunded multiple assets
  23 type RefundAssets []*bc.AssetAmount
  24
  25 // FeeStrategy used to indicate how to charge a matching fee
  26 type FeeStrategy interface {
  27         // Allocate will allocate the price differential in matching transaction to the participants and the fee
  28         // @param receiveAmounts the amount of assets that the participants in the matching transaction can received when no fee is considered
  29         // @param priceDiffs price differential of matching transaction
  30         // @return reallocated assets after calculating fees
  31         Allocate(receiveAmounts, priceDiffs []*bc.AssetAmount) *AllocatedAssets
  32
  33         // Validate verify that the fee charged for a matching transaction is correct
  34         Validate(receiveAmounts []*bc.AssetAmount, feeAmounts map[bc.AssetID]uint64) error
  35 }
  36
  37 // DefaultFeeStrategy represent the default fee charge strategy
  38 type DefaultFeeStrategy struct {}
  39
  40 // NewDefaultFeeStrategy return a new instance of DefaultFeeStrategy
  41 func NewDefaultFeeStrategy() *DefaultFeeStrategy {
  42         return &DefaultFeeStrategy{}
  43 }
  44
  45 // Allocate will allocate the price differential in matching transaction to the participants and the fee
  46 func (d *DefaultFeeStrategy) Allocate(receiveAmounts, priceDiffs []*bc.AssetAmount) *AllocatedAssets {
  47         feeMap := make(map[bc.AssetID]uint64)
  48         for _, priceDiff := range priceDiffs {
  49                 feeMap[*priceDiff.AssetId] = priceDiff.Amount
  50         }
  51
  52         var fees []*bc.AssetAmount
  53         refunds := make([]RefundAssets, len(receiveAmounts))
  54         receives := make([]*bc.AssetAmount, len(receiveAmounts))
  55
  56         for i, receiveAmount := range receiveAmounts {
  57                 amount := receiveAmount.Amount
  58                 minFeeAmount := d.calcMinFeeAmount(amount)
  59                 receives[i] = &bc.AssetAmount{AssetId: receiveAmount.AssetId, Amount: amount - minFeeAmount}
  60                 feeMap[*receiveAmount.AssetId] += minFeeAmount
  61
  62                 maxFeeAmount := d.calcMaxFeeAmount(amount)
  63                 feeAmount, reminder := feeMap[*receiveAmount.AssetId], uint64(0)
  64                 if feeAmount > maxFeeAmount {
  65                         reminder = feeAmount - maxFeeAmount
  66                         feeAmount = maxFeeAmount
  67                 }
  68
  69                 fees = append(fees, &bc.AssetAmount{AssetId: receiveAmount.AssetId, Amount: feeAmount})
  70
  71                 // There is the remaining amount after paying the handling fee, assign it evenly to participants in the transaction
  72                 averageAmount := reminder / uint64(len(receiveAmounts))
  73                 if averageAmount == 0 {
  74                         averageAmount = 1
  75                 }
  76
  77                 for j := 0; j < len(receiveAmounts) && reminder > 0; j++ {
  78                         refundAmount := averageAmount
  79                         if j == len(receiveAmounts)-1 {
  80                                 refundAmount = reminder
  81                         }
  82                         refunds[j] = append(refunds[j], &bc.AssetAmount{AssetId: receiveAmount.AssetId, Amount: refundAmount})
  83                         reminder -= averageAmount
  84                 }
  85         }
  86         return &AllocatedAssets{Receives: receives, Refunds: refunds, Fees: fees}
  87 }
  88
  89 // Validate verify that the fee charged for a matching transaction is correct
  90 func (d *DefaultFeeStrategy) Validate(receiveAmounts []*bc.AssetAmount, feeAmounts map[bc.AssetID]uint64) error {
  91         for _, receiveAmount := range receiveAmounts {
  92                 feeAmount := feeAmounts[*receiveAmount.AssetId]
  93                 maxFeeAmount := d.calcMaxFeeAmount(receiveAmount.Amount)
  94                 minFeeAmount := d.calcMinFeeAmount(receiveAmount.Amount)
  95                 if feeAmount < minFeeAmount || feeAmount > maxFeeAmount {
  96                         return ErrAmountOfFeeOutOfRange
  97                 }
  98         }
  99         return nil
 100 }
 101
 102 func (d *DefaultFeeStrategy) calcMinFeeAmount(amount uint64) uint64 {
 103         return uint64(math.Ceil(float64(amount) / 1000))
 104 }
 105
 106 func (d *DefaultFeeStrategy) calcMaxFeeAmount(amount uint64) uint64 {
 107         return uint64(math.Ceil(float64(amount) * 0.05))
 108 }